Are air source heat pumps noisy? What UK households should know

What to know first

These points explain heat-pump sound and the permitted-development route, which may avoid a full planning application when every applicable condition is met.

Air source heat pumps are not silent. Their outdoor units move air and contain a compressor, so a fan-like hum and changes in pitch are normal. A suitable unit should be positioned and assessed to limit its effect at nearby living rooms and bedrooms.

The result depends on the machine, operating demand, distance, reflecting surfaces, barriers, mounting and local background sound. One decibel figure can mislead unless it says what was assessed and where.

A government review published in November 2023 found concern among a minority of participants and a low incidence of complaints. It linked complaints mainly to poor installation, location or proximity, but did not establish a national complaint rate.

How loud is an air source heat pump?

There is no single figure for every heat pump or home. The model, operating condition and place of assessment all matter.

The Microgeneration Certification Scheme, or MCS, sets standards used in the planning calculation. Sound power is the total sound energy radiated by the source. Sound pressure is the sound at a point. Put simply, sound power belongs to the machine; sound pressure is what reaches a location.

These definitions and the 37 dB(A) assessment basis come from MCS 020(a).

MCS 020(a) uses an A-weighted sound-power value from the product fiche, energy label or MCS database. A-weighting approximates human hearing. The calculation then allows for distance, reflecting surfaces and qualifying barriers.

A quiet setting may lower fan and compressor speed temporarily. It may also reduce output, hot-water recovery or efficiency, so the design should not depend on that setting to meet the planning test.

Why can the sound change at night or in cold weather?

A heat pump does not make one fixed sound. It may be more noticeable in harsh weather, while making hot water, during defrost or when maintenance is needed.

Defrost is a normal temporary cycle that clears ice from the outdoor coil. A persistent rattle, buzz or sudden new noise instead deserves investigation for loose parts, debris, maintenance problems or faults.

At night, a sound that blended into traffic or daytime activity may stand out.

Intermittent or tonal sound can also attract attention, and people differ in sensitivity. Two people may therefore react differently to the same installation.

What makes heat pump sound more noticeable to neighbours?

Positioning changes what reaches a nearby window. The MCS calculation and guidance reflect these main factors.

The table is a starting point rather than a property assessment. The calculation must use the actual unit, position, surrounding surfaces and neighbouring openings.

Vegetation and open or damaged fences do not count as barriers in the MCS calculation. A qualifying barrier must be solid and gap-free, and its effect depends on whether it blocks the line of sight. It must not obstruct airflow, safe access or warranty requirements.

Expert insight

“Do not compare products only by the lowest brochure number. Ask which sound-power value was used, which doors and windows were assessed, and how the proposed position affects the calculation.”

Giles Crosse

Energy Editor

Experienced editor, journalist and communications consultant specialising in consumer energy and low carbon technologies.

• Editor and campaign author for Shell, EDF Energy and Good Energy.
• Consultant to the United Nations and contributor to the World Economic Forum.
• Journalist for Reuters, the BBC, The Economist and The Guardian.

More about Giles Crosse

What does the planning noise check actually assess?

MCS 020(a) checks for no more than 37 dB(A), averaged over five minutes, at each relevant assessment position. It excludes the extra reflection from the receiving building’s external wall.

An assessment position is one metre outside the centre of a door or window serving a neighbouring habitable room. This means a room used for living or sleeping, not a bathroom, corridor or utility room. Every potentially affected position should be considered.

The calculation records source sound power, reflections, distance and any qualifying barrier. MCS contractors must give the customer a copy. A result of 37.0 dB(A) or below at every position meets the sound part of the test, but not every other planning condition.

The published position differs across the UK:

• England: permitted-development rules have referred to MCS 020(a) since 29 May 2025.

• Wales: Welsh Government information updated in 2026 requires MCS 020(a).

• Scotland: published guidance refers to MCS 020 or an equivalent standard.

• Northern Ireland: the 2023 order names MCS 020 Issue 1.3 and retains a one-metre boundary condition. The government’s current legislation list was checked for later changes.

Practical interpretation, checked 5 August 2026: confirm the applicable standard and all other conditions with the local planning authority. Passing the sound check does not promise that nobody will hear the unit, and MCS 020(a) does not by itself grant permitted-development rights.

How can noise risk be reduced before installation?

Noise is easiest to address while the product and position can still change.

1. Map sensitive openings. The designer should identify neighbouring living-room and bedroom doors and windows at every relevant floor, not just measure to the boundary.

2. Use the correct figure. The designer should record the A-weighted sound-power value and its source. A generic “noise level” is insufficient.

3. Compare positions. Moving the unit changes distance, reflections and line of sight. The household can ask to see how alternatives affect the calculation and access.

4. Specify any barrier. The designer should check solidity, height, airflow, service access and warranty implications. A hedge does not count.

5. Keep the evidence. The installer should provide the calculation, model details, site plan, barrier assumptions and commissioning records. The household should retain them.

A completed sound calculation supports the noise assessment. It does not, by itself, secure permitted-development status or planning approval.

Good to know

Do not build a makeshift box around the unit. Noise measures must not impair operation or safety, unnecessarily reduce performance or invalidate the warranty. Consult the manufacturer where there is doubt.

A competent heat-pump designer or installer should prepare the calculation. A tight, unusually quiet or complex site may also justify an acoustic consultant, meaning a noise specialist, and contact with the local planning authority.

What should happen if a heat pump becomes intrusive?

Record when the sound occurs, its character, the weather and whether the unit is making hot water or defrosting. This can help separate normal changes from a fault.

The owner or service engineer can check for debris, loose parts, damaged mounts, overdue maintenance and changes to a barrier. Leave internal electrical and refrigerant components to an appropriately competent person.

A calm conversation may identify one troublesome operating period. An installer may be able to adjust scheduling or controls without compromising heating or hot water.

If the problem remains, the planning authority can consider planning compliance. The council’s environmental-health or noise service can explain its complaint process. These are separate assessments, and official routes differ across the UK.

Key takeaways

• No single figure predicts what every household or neighbour will hear.

• Sound power rates the source; sound pressure describes sound at a location.

• England and Wales use a 37 dB(A) MCS 020(a) calculation at defined positions.

• Night-time quiet, cold conditions, hot-water operation and defrost can make sound more noticeable.

• Distance, reflections, barriers, orientation and vibration control should be designed before installation.

• Keep the calculation and investigate new rattling, buzzing or a marked change in noise.

Frequently asked questions